The present invention generally relates to wireless communication devices and, more particularly, to bypassing a power amplifier in a wireless communication device communicating with an access point in a local area network (LAN).
Wireless communication devices, for example devices using radio frequency signal transmission, generally must comply with regulations limiting, for example, the radio frequency emissions, transmit power, and mode of operation of the devices. Such regulations may be enforced by the Federal Communications Commission (FCC) in the United States, for example, or in Europe by the European Telecommunications Standards Institute (ETSI). Wireless LAN communication networks are subject, for example, to the IEEE 802.11 standard, which includes, for example, 802.11a, 802.11b, and 802.11g standards. The 802.11b standard limits transmit power for wireless LAN communication devices in the United States to 30 decibels relative to one milliwatt (dBm), in Europe, to 20 dBm, and in Japan, to 10 dBm per megaHertz (dBm/MHz). Such wireless LAN communication devices may be described as stations or access points. Stations typically may be found in laptop computers, cell phones, portable modems, or personal digital assistants (PDAs), where they are used for communication with a wired LAN through an access point, which may be generally described as a wireless transmitter/receiver connected into the wired LAN for interfacing the wired LAN to the wireless communication devices. Stations may also communicate with other stations in a peer-to-peer network, without the presence of an access point, described in the IEEE 802.11a, 802.11b or 802.11g standard as “ad-hoc” mode.
The 802.11 standard specifies a half-duplex mode of operation for wireless transmitter-receivers, also commonly referred to as “transceivers”, included in wireless LAN communication devices. Half-duplex operation is characterized by the transceiver, at any given time, either transmitting a signal or receiving a signal, but not both. Half-duplex operation is distinguished from full-duplex operation in which the transceiver may simultaneously transmit one signal while receiving a second signal. Half-duplex operation typically requires control by the communication device as to whether the transmitter or the receiver is either operating or has an access to the communication channel. As illustrated by FIG. 1, for example, the control over access to the communication channel may be accomplished by switching the connection of the antenna of the wireless communication device between the receiver and the transmitter of the device.
FIG. 1 shows an example of a wireless LAN communication device 100 developed in accordance with the IEEE 802.11a, 802.11b or 802.11g standard. The communication device 100 includes an antenna 101 for receiving and transmitting signals. The antenna 101 is connected to an RF filter 103 for filtering jammer signals. The RF filter 103 is coupled to a switch 104 that switches between signal paths 104a and 104b. The switch 104 selects the signal path 104a when the communication device 100 is receiving a signal. The received signal is propagated from the switch 104 to a low noise amplifier (LNA) 106 that amplifies the received signal. The output signal of the LNA 106 is processed by an RF receiver 109. The processed signal is transmitted to a modem 111. An RF transceiver chip 112 contains the LNA 106, the RF receiver 109, a power amplifier 107, a switch 108 and an RF transmitter 110.
On the other hand, when the communication device 100 transmits a signal, the switch 104 switches to the signal path 104b that is connected to a switch 105. The switch 105 works in conjunction with the switch 108 to bypass the power amplifier 107 when the communication device 100 is transmitting a signal. When the communication device 100 is transmitting a signal, a signal from the RF transmitter 110 is received by the switch 108, and the switch 108 switches to a signal path 105a if the power amplifier 107 is bypassed but switches to a signal path 107a if the signal from the RF transmitter 110 needs to be amplified by the power amplifier 107. The output of the power amplifier 107 is connected to the signal path 105b. In certain situations, the power amplifier 107 needs to be bypassed because the amplification by the power amplifier 107 may create a signal that interferes with other signals due to the strength of the signal. Such situations may occur if the communication device 100 is close to an access point or a base station. In other situations, the power amplifier 107 is bypassed to conserve battery power.
If the signal from the RF transmitter 110 needs to be amplified, the switch 108 switches to the signal path 107a, and the power amplifier 107 receives the signal and amplifies the signal. The amplified signal is received by the switch 105 through the signal path 105b. 
Since the switch 105 may receive and propagate an amplified signal to the switch 104, the switch 105 must meet certain strict linearity requirements or the amplified signal will become distorted by the switch 105. In order to meet such strict linearity requirement, the switch 105 cannot be integrated into the RF transceiver chip 112 because the switch 105 may require different fabrication process (such as a GaAs process as opposed to the SiGe process used for the RF tranceiver chip 112). Since the switch 105 is external to the RF transceiver chip 112 and requires a different fabrication process from the RF transceiver 112, the fabrication of the switch 105 incurs extra costs and extra board space.